Electrical signal amplifying apparatus



Nov. 15, 1932. w. L. CARLSON ET AL ELECTRICAL SIGNAL AMPLIFYINGAPPARATUS Filed July 6, 1928 lnventor-$= Wendell. I... Carlson. DonaLdwlLson,

WWI/M His Attorney.

Patented Nov. 15, 1932 1 UNITED S AT S marsh earer was WENDELL L.CARL-SON AND IDGNALD WILSON, 0F SCHENEGTADY, ITEW YORK, ,ASSIGNORS TOGENERAL ELECTRIC COMPANYQA CQRPORATIGN OF NEW YORK ELECTRICAL SIGNAL AMP'I Yrn APPARATUS Application filed July 6,

Our invention relatesto electrical signal amplifying apparatus embodyingelectric discharge devices and more particularly to an apparatus of thischaracter in which the anode, cathode and gridv bias voltages for suchelectric discharge devices are taken wholly or in part from a commonsupply means. With improved coupling means in such apparatus as, forexample, improved audio frequency transformers and resistance couplingdevices in a sound amplifying ap paratus, and a common source of energyfor the various coupled circuits and electric discharge devices therein,a varying current of relatively low frequency often builds up in theoutput circuit and with a sound reproducer therein causes a persistentfluttering or motor boating noise in the latter. This may be caused bypoor voltage regulation at the supply terminals, acoustic feedback,overloading the output tube, an undesirable coupling between the variouscircuits through the common supply means, or a combination of thesecauses.

Poor regulation, that is, the inability to hold substantially constantsupply voltage with varying load is caused by'high internal resistanceat some point in the supply circuit. This is a salient characteristic ofthe usual rectified alternating current source of energy now commonlyused with apparatus embodying electric discharge devices. The resistancemay become a common coupling means for a plurality of circui s and in anamplifier circuit for sound amplification and reproduction, for example,may be: come the source of troublesome audible fluttering or motorboating as above mentioned. In other apparatus of this character, alottering or varying output, while not necessarily audible, isnevertheless highly undesirable.

It is therefore the object of our invention to provide an improvedcircuit arrangement for supplying energy from a common means havingrelatively poor voltage regulation to a plurality of electric dischargedevices in an electrical amplifying appa ratus without obtaining anundesirable fluctuation in the output circuit of such apparatus. T

1925i Serial No. 299,803.

Our invention will be better understood from the following descriptionwhen considered in connection with the accompanying drawing, and itsscope will be pointed out in the appended claims.

7 In the drawing, the single figure is a wiring diagram ofanapparatus'embodying our invention. Byway of example, and not in any wayas indicating a limitation in the application of our invention, this isa wiring diagram of a radio receiving set provided with a plurality ofreceiving and amplifying electric discharge devices 5 of the vacuum tubetype having cathode and control grid connection with a tapped cathodeand grid voltage supply resistor 6, and anode connection with high andlow voltage supply'leads 7 and 8. The usual apparatus in the anode andgrid circuits of these devices is'notshown as it does not concern the invention and the diagram is greatly simplified and more readilyunderstood by its omission.

Anode supply leads 7 and 8, together with an anode return lead '9,connect with a tapped plate supply or anode resistor 10. Lead 9 inefiect connects resistors 6 and 10 in series and they are then connectedin this relation with suitable high voltage direct current supplyterminals 11 and 12, the polarity of which is indicated the drawing.This represents'a known voltage divider resistor arrangement in anapparatus of this character for obtaining anode, cathode and biasvoltages from a common high voltage direct current source. I

In the present example, the high voltage direct current is obtained fromrectified and filtered alternating current through a commen and wellknown rectifier and filter apiaratus represented by transformer 13,rectiiiers let andfilt-er choke'and capacities 15 and 16 respectively.

- Alternating current of the usual commercial voltage and frequency issupplied from lines 17 and after being stepped up by the transformerisrectified at 14c and passed through filter 1516 to the supply terminals11' and 12' The voltage regulation at terminalsll and 12 depends uponthe load drawn by the apparatus connected therewith because of theinherently poor regulation caused for the most part by the internalresistance of rectifiers 14; and of the filter choke 15, and this supplymeans may be taken as terminals 11 and 12 with the varying'load taken bythe apparatus connected therewith and because plate current variationsof the power or output tube 18 cause'fiuctuations of thefilament-emission of amplifier tubes 5 which in turn cause voltagefluctuations to be transmitted to'the power tube either directly by theaudio amplifier or by modulation of the carrier wave being received.This is carried through to the power tube 18, which 3 in the presentexample is coupled with the amplifying and receiving apparatus by asuitable transformer or other coupling device 19, the secondary of whichis'connected with the grid circuit 20 of the power tube.

These variations are then transmitted to apparatus connected with anoutput circuit 21 which in the present example is connected through asuitable output: transformer 22 with the output oranode circuit 23 ofthe power tube. When asshown, the output circuit supplies a soundproducer or loud speaker indicated at 24, the fluttering or varyingoutput curr nt in anode circuit 23 is reproduced by the loud speaker.

In accordance with our invention, however, we arrange the anode circuitof the output or power device 18 in such a manner that the anode orplate current therefor does not flow through either the anode or thefilament circuits of the preceding amplifying devices 5, that is, in thepresent example, the anode circuit of tube 18 is so arranged that itdoes not include resistor 6 and the filament circuits of the precedingtubes 5.

In carrying out this improved circuit arrangement, the high potentialside of the output anode circuit 23 connects with the high potentialsupply terminal 12 through a supply lead 25 while a cathode return lead26 for this circuit connects with the low potential supply, terminal 11.The grid-circuit 20 returns to the samepoint through a return lead 27,and a suitable resistor 28 in lead 26 bypassed by a capacity 29, servesto effect the proper bias on the grid of the power or output device 18.The cathode of this device is heated from a separate source which in thepresent example is a mid-tapped low voltage secondary 30 on the powersupply transformer 13.

Interposed between the high potential supply terminal 12 and the voltagedivider resistor, in such a manner that it is included in the voltagedivider circuit, is an impedance or choke coil 31 which may be of anysuit able construction having a relativelylow resistance and arelatively high impedance to current fluctuations. This choke coil ispreferably by-passed on its low potential side to the low potentialsupply terminal 11 by a condenser or capacity 32 of relatively highvalue corresponding to those used in the filter at 16, and together withthe choke coil providesa low frequency filter for the voltage dividercircuit 109-6 and the anode and cathode supply circuits connectedtherewith. The use of a'high impedance interposed in the voltage dividercircuit in series with the Volt age divider resistance tends to reduce.the hum in connected apparatus, such as the reproducer 24, resultingfrom such current fluctuations.

The choke coil or impedance and series connected voltage dividerresistance for the anode and plate may be considered to form anindependent shunt circuit across the supply terminals 11 and 12. Viewedin another .aspcct the plate circuit of power or output tube 18 isconnected between the choke coils 1'5 and 31 whereby the output tubeconnection is separated from the voltage divider resistor by the latterchoke coil.

lVith rectified alternating current as the power source it is desirableto shunt the filament and grid bias portion of the resistor for zdirectly with the supply terminals and'not into or through theseresistors or any part thereof. Thus none of the output anode currentflows in the voltage divider resistor or in the circuits with which itis connected, that is, in either the anode or the cathode circuits ofthe preceding electric discharge devices of the amplifying apparatus.

This circuit arrangement has been found to eliminate the flutteringcharacteristic in and has resulted in satisfactory and stable operationof apparatus of the character described permitting the use of a commonsupply source for the anode circuit of an output tube and the filamentand plate supply of preceding tubes, without being. affected by thenormal regulation of such supply source.

lVha-t we claim as new and desire to secure by Letters Patent of theUnited States, is:

1. In an amplifying apparatus, a pair of high voltage supply terminals,a voltage divider resistor connected across said terminals, a cathodesupply circuit connected in shunt with at least a portion of saidresistor, and an output electric discharge device having an anodecircuit connected with said supply terminals independently of saidresistor whereby the anode current for said device flows directly fromsaid terminals without passing through said resistor and the cathodesupply circuit.

2. In an amplifying apparatus having a pair of high voltage supplyterminals, the combination ofa voltage divider resistor connected acrosssaid terminals, a cathode supply circuit connected in shunt with atleast a portion of said resistor, an output electric discharge devicehaving an anode circuit connected with said supply terminalsindependently of said resistor, and means providing a relatively highimpedance to current fluctuations connected between said resistor andone of said terminals.

3. In an amplifying apparatus embodying electric discharge devices andhaving high voltage supply terminals, the combination of an outputcircuit connected directly with said terminals, a plurality of anodecircuits, a cathode heating circuit, and voltage divider means throughwhich said anode and cathode heatingcircuits are connectedwith saidterminals independently of said output circuit.

4. In an amplifying apparatus embodying a plurality of electricdischarge devices, the

combination with common high voltage supply terminals for said devices,of an output :ircuit connected directly with said terminals. a pluralityof anode circuits, an anode supply resistor through which said anodecircuits are connected with said terminals, a cathode supply resistor inseries with the anode supply resistor at the low potential end thereof,and a plurality of oath-odes connected with said cathode supplyresistor.

5. In an amplifying apparatus embodying 7 electric discharge devices,the combination of an anode supply resistor, a cathode supply resistor,said resistors being connected in series, a high potential supplyterminal with which the first named resistor is connected, a lowpotential supply terminal with which the second named resistor isconnected, an output anode circuit having asupply lead connected withthe high potential supply terminal and a cathode return lead connectedwith the low potential supply terminal whereby said circuit is connectedwith said terminals in parallel with said series connected resistors.

' 6. In an amplifying apparatus embodying electric discharge devices andhaving high voltage supply terminals, the combination of an output anodecircuit connected directly with said terminals, a plurality ofadditional anode circuits, a cathode heating circuit, voltage dividermeans through which said anode and cathode heating circuits areconnected with said terminals independently of said output circuit, andan impedance means cone nected between said output anode circuit andsaid voltage divider means in circuit with the latter.

7. The combination of a pair of interconnected electric dischargedevices, a power supply circuit, and a filter means provided with endterminals connected respectively to said circuit and to the outputcircuit of one of said devices and with an intermediate terminalconnected to the output circuit of the other of said devices whereby theoutput circuits of said devices are isolated from each other, saidfilter means including an imped ance element connected in series withsaid output circuit of said one of said discharge devices, saidimpedance element being characterized by relatively low resistance todirect current and relatively high impedance to the alternatingcomponents of current in said power supply circuit. p

8. In an apparatus embodying electric discharge devices, the combinationof an output device therefor, having a grid circuit, a second devicehaving an anode circuit coupled with said grid circuit, means providinga supply circuit in connection with said last named device for supplyingelectrical energy thereto, a filter means in said circuit for smoothingthe flow of energy therethrough, and an output anode circuit for saidoutput device connected with said filter intermediate its ends forreceiving energy therefrom, whereby said anode circuit is isolated fromsaid supply circuit and hum eiiects in the output of said output deviceare obviated.

In witness whereof, we have hereunto set our hands this th day of June1928.

WVENDELL L. GARLSON. DONALD WILSON.

